The present invention relates to a phase change mechanism.
A phase change mechanism is known for enabling the phase of an engine camshaft to be changed in relation to the engine crankshaft. The known mechanism comprises a drive member connectable for rotation with the engine crankshaft, a driven member connectable for rotation with the engine camshaft and two oppositely acting one-way clutches for transmitting torque from the drive member to the driven member. To bring about a phase change, means are provided for selectively disengaging one of the one-way clutches at a time. This allows the drive member to slip relative to the driven member in the desired direction as a result of the periodic reversal of the reaction torque of the camshaft during engine operation.
In the known phase change mechanism, the means for disengaging one of the two one-way clutches at a time acted mechanically on the components to the clutch and a complex control system was required for setting the desired of the drive member relative to the driven member.
According to the present invention, there is provided a phase change mechanism for enabling the phase of an engine camshaft to be changed in relation to the engine crankshaft, the mechanism comprising a drive member connectable for rotation with the engine crankshaft, a driven member connectable for rotation with the engine camshaft, two oppositely acting one-way clutches for transmitting torque from the drive member to the driven member, and means for, applying hydraulic pressure directly to the locking elements of the one-way clutches for selectively, disengaging one of the one way clutches at time to allow the drive member to slip relative to the driven member solely under the action of the periodic reversal of the reaction torque of the camshaft during engine operation.
The two one-way clutches may suitably be constituted by at least one pair of cylindrical rollers serving as the locking elements and arranged between a cylindrical race on one of the members and tow ramp surfaces on the other member, the rollers being urged apart by a spring that acts to wedge each roller between the cylindrical race and a respective one of the ramp surfaces.
The means for disengaging each clutch preferably comprise means for subjecting one of the rollers of each pair to hydraulic pressure on its opposite side from the spring so as to move the roller away from wedging contact with the respective ramped surface.